1. Technical Field of the Invention
The present invention relates to electrical rotating machines, whether motors or generators, and more precisely to the stators thereof.
2. The Related Art
In a known construction, the stator of machines of the foregoing type has a magnetic circuit and windings of electrically conductive wires which in general are made from insulated copper wire, often round in cross section. The magnetic circuit, for its part, is laminated; i.e., it is formed by a stack of magnetic metal sheets. Each metal sheet is cut to shape such that slots delimited by teeth are made, the slots being the seatings for the electrically conductive wires. This principle of arranging the stator is widely applied in synchronous or asynchronous machines.
There are applications for which it is desirable to simultaneously obtain both high power levels and highly compact constructions of the motor. To give just one concrete example, when the intention is to install electric traction motors in the wheels of automotive vehicles, it is desirable to be able to develop power levels of at least 10 kW per motor, and even at least 25 or 30 kW per motor for the majority of the time, for a weight as low as possible in order not to make the unsprung masses too heavy. It is also desirable for the bulk to be very small, not going beyond or going beyond by as little as possible, the internal volume of the wheel, so that the motor does not interfere with the elements of the vehicle in the event of flexing of the suspension and in the event of other types of movement of the wheel with respect to the vehicle body.
These requirements (high power level and low weight and bulk) make it very problematic to install electric traction motors in the wheels of private vehicles without radically improving the ratio of weight to power of the electrical machines currently available on the market.
Moreover, the heating caused by losses of the motors must be contained within certain limits, or else irreversible degradation occurs, in particular with respect to the insulation of the electrical conductors. The heat produced in the stator conductors must thus be dissipated as effectively as possible.
In the most demanding applications, it is already well known to cool electrical rotating machines by means of a liquid. In this case, forced circulation of the liquid is provided within the electrical rotating machine itself, principally the stator, in which the electrical windings are located, so that the heat is guided out to a heat exchanger.
In order properly to hold the electrical conductors mechanically in their slots, to; reinforce the electrical insulation and indeed to contribute to good heat exchange by conduction, it is already known to impregnate the electrical conductors in resin, which fills the various slots and covers the winding heads on either side of the stator.
Unfortunately, although impregnation of the conductors with resin proves indispensable in high-performance motors, the resins used to impregnate the conductors in the slots are materials which are relatively poor heat conductors. It is also known to use resins containing fillers, which are better conductors of heat, to impregnate the conductors of the winding heads. Unfortunately, the resins used in the winding heads are not suitable for impregnating the conductors in the slots. The fillers cannot penetrate into the small spaces remaining in the slots, and this is all the more true in high-performance motors because a high level of filling the slots with copper is sought.
Furthermore, dissipation of the heat produced in the slots is problematic. In fact, there are currently faults in the impregnation; in other words, bubbles (of air or degassing products) remain trapped inside the mass of the conductors and resin. The consequence is that the heat exchange taking place where these faults in the impregnation exist is much less effective, since it cannot take place by conduction. The result is a local rise in temperature, which can have an adverse effect on the proper behaviour of the electrical insulating materials used and, as a consequence, cause thermal breakdown phenomena in the electrical rotating machines.
One object of the invention is to radically improve the heat performance of electrical rotating machines.
Another object is to bring about the much more homogeneous and improved quality impregnation of the electrical conductors in the slots.
A further object is to allow impregnation by a resin which is a sufficiently good beat conductor.
This is most particularly important if the rated torque of an electrical rotating machine is to be increased. To this end, the aim is to be able to introduce as high a current as possible. The consequence is inevitably Joule""s heat losses, as a result of which heat is produced in the conductors located in the slots and in the winding heads and has to be dissipated as effectively as possible.
The invention relates to an electrical rotating machine comprising a stator, the stator comprising a laminated magnetic circuit having a stack of magnetic metal sheets disposed substantially parallel to a plane perpendicular to the axis of rotation of the rotor of the machine, the magnetic circuit having a plurality of teeth, the teeth delimiting longitudinally oriented slots, electrically conductive wires being disposed in the slots, the ratio of the sum of the sections of the squares circumscribing the section of each conductive wire to the useful slot section being greater than 0.7 for each slot. The electrical wires are kept immobile in the slots by a slot-impregnating composition containing a heat-setting resin and a filler, which slot-impregnating composition comprises at least 65% by mass of the filler.
The ratio indicated above denotes a very high level of filling the slots with the conductive wires. Machines of high specific output are to be constructed.
In a first aspect, the particle size of the slot-impregnating composition is such that the average size of the particles of which it is composed is less than approximately 15 xcexcm, and is such that at least approximately 80% by mass of the particles are less than 25 xcexcm in size.
In fact, the nature of the filler indicated above is not unrelated to the diameter or, more generally, the size of the section of the conductive wires used. If the nature indicated is very well matched to wires having a diameter in the order of 1.2 mm to 1.5 mm, which are themselves well matched to the machines of high specific output to which the invention relates, one may also take the view that, in another aspect, the particle size of the filler is such that the maximum size of the particles of which it is composed is less than 0.045*xcfx86, where xcfx86 is the diameter of the electrically conductive wires disposed in the slots.
Preferably, the particle size of the filler is such that at most 3% by mass of the particles are above 50 xcexcm in size.
This filler is preferably silica flour (silicon oxide), quartz (a crystalline form of silica), aluminum nitride or alumina. It has been found that these fillers radically improve the performance levels of an electrical machine, in particular when they are used in accordance with the process below.
It is also known that the stator has winding heads at the two axial ends of the magnetic circuit The invention also relates to an electrical rotating machine in which the conductors in the winding heads are impregnated with a composition for impregnating winding heads which contains a heat-setting resin and a filler of larger particle size than the particle size of the filler of the slot-impregnating composition.
To clarify these concepts, the difference in particle size can be qualified by reference to the size of the particles and their distribution over different sizes. For example, the filler of large particle size has approximately from 30 to 55% by mass of particles having a size between 500 xcexcm and 1000 xcexcm; it has approximately from 25 to 45% by mass of particles having a size between 200 xcexcm and 600 xcexcm, with the remainder being composed of at least 5% by mass of particles of which at least 80% by mass are below 25 xcexcm, and preferably below approximately 20 xcexcm in size, and at most 3% by mass are above 50 xcexcm, and preferably above approximately 45 xcexcm in size.
For its part, the filler of lower particle size is characterized by an average size of the particles of below approximately 15 xcexcm, and preferably below approximately 10 xcexcm, and has at least approximately 80% by mass of particles of which the size is below 25 xcexcm, and preferably below approximately 20 xcexcm, and has no more than approximately 3% by mass of particles of which the size is above 50 xcexcm, and preferably above approximately 45 xcexcm.
It has been found that a filler of the foregoing kind allows the thermal conductivity of the slot-impregnating composition to be improved, and that the improvement in the properties of thermal conductivity of the composition is not accompanied by a disadvantageous increase in the viscosity of the composition.
Preferably, in order to achieve values for thermal conductivity which are really very high for a slot-impregnating material, the slot-impregnating composition comprises at least 70% by mass of the filler.
The invention also proposes a process for manufacturing a stator of an electrical rotating machine, the stator comprising a laminated magnetic circuit having a stack of magnetic metal sheets disposed substantially parallel to a plane perpendicular to the axis of rotation of the rotor of the machine, the magnetic circuit having a plurality of teeth, the teeth delimiting longitudinally oriented slots, the process comprising the following steps:
installing electrically conductive wires in the slots and forming winding heads at the two axial ends of the magnetic circuit;
installing on a vertical axis the assembly having the magnetic circuit supporting the conductors in the slots and the winding heads;
impregnating under vacuum the conductors in the slots with a slot-impregnating composition comprising a heat-setting resin and a filler; and
proceeding to polymerisation of the composition.
In order to use impregnating compositions, both containing fillers and differing at least in their fillers, the invention proposes a process for manufacturing a stator of an electrical rotating machine, the said stator comprising a laminated magnetic circuit having a stack of magnetic metal sheets disposed substantially parallel to a plane perpendicular to the axis of rotation of the rotor of the machine, the magnetic circuit having a plurality of teeth, the teeth delimiting longitudinally oriented slots, the process comprising the following steps:
installing electrically conductive wires in the slots and forming winding heads at the two axial ends of the magnetic circuit;
installing on a vertical axis the assembly having the magnetic circuit supporting the conductors in the slots and the winding heads;
impregnating the first winding head, in an axially upper position, with a composition for impregnating winding heads, comprising a heat-setting resin and a filler of large particle size;
turning around the assembly and installing it once again on a vertical axis, so that the first winding head becomes the lower winding head;
impregnating under vacuum the conductors in the slots with a slot-impregnating composition comprising a heat-setting resin and another filler of smaller particle size than the particle size of the filler of the first composition;
impregnating the second winding head with a composition for impregnating winding heads, comprising a heat-setting resin and a filler of large particle size; and
proceeding to polymerisation of the compositions.